Mineral composition and biomass partitioning of sweet sorghum grown for bioenergy in the southeastern USA

Biomass yield and tissue mineral composition can affect total energy yield potential, conversion efficiencies and environmental impacts, but relatively few data are available for sweet sorghum [Sorghum bicolor (L.) Moench] grown in the southeastern USA. Therefore, a study was conducted at two locations in North and Central Florida on marginal sand soils comparing the effects of planting date (PD) on dry biomass yield and mineral composition of leaf, stem, and grain heads for ‘M-81E’ and ‘Dale’ sweet sorghum cultivars. Overall tissue mineral concentrations were relatively low for sweet sorghum, attributable to low K and Ca concentrations. Ash and mineral concentrations were generally greater for Dale, especially for the early PD. Leaf and grain heads were greater in mineral concentrations compared to stems. Dry biomass yield averaged 19.4 Mg ha−1 and was greater for M-81E and the early PD. Stems accounted for 73% of the total biomass compared to leaves (13%) across all treatments. Total N, P, and K removals averaged 136, 27.6, and 81.4 kg ha−1, respectively. Overall, leaves removed 30, 23, and 19% of total N, P, and K compared to 34, 34, and 61% by stem, respectively. Considering lower biomass but greater mineral concentrations in leaf and grain heads compared to stems, returning leaf residues and possibly grain heads to the soil have the potential to offset nutrient and energy inputs needed on these marginal soils and enhance the sustainability of sweet sorghum cropping systems.